Patent GB-530565-A (GB)
Title: Improvements in screw thread cutting machines
IPC: B23G1/02
Filed: 1939-06-27
Abstract: 530,565. Lathes. CASTELLI, X. F. June 27, 1939, No. 18756. Convention date, June 28, 1938. [Class 83 (iii)] In a screw-cutting lathe the main driving shaft actuates the longitudinal strokes of the tool-holder and also operates a stepped cam such as a disc having bosses for causing the tool to penetrate deeper into the work at each stroke. The tool 19 is mounted in a holder 20 set relatively to the lathe axis by micrometer screws 25 and a bar 24 carrying a roller 27 engaging a lever 33 whose other arm is kept by a spring against a stepped cam 35, the steps of which determine the depth of cut at each longitudinal traverse. A cam plate 18 carried by a vertical slide 14 has an inclined side engaging a roller 42 on a vertically adjustable slide 43 mounted on the longitudinal saddle 23 carrying the holder 20. In operation, the diameter of cut is determined by the screws 25 and the machine is started by operating a lever 5 to move a belt 6 on to a fast pulley 3. The cam 12 moves the slide 14 upwards during 270 degrees of its rotation and the cam plate 18 thus feeds the saddle 23 longitudinally to form a cut in the work of the required pitch. A dog 36 on the cam 12 then actuates a pawl 38 through a lever 37 to rotate the cam 35, thus allowing the lever 33 to drop into a recess of the cam and withdraw the cutter from the work. Further rotation of the cam 12 allows the slide 14 to fall and the tool is moved rapidly back to its starting point, and just before the cam 12 commences its next rotation a second dog 36 thereon actuates the pawl 38 to rotate the cam 35 and move the next highest step thereof under the lever 33, thereby feeding the tool in for a deeper cut on the next traverse. When the cam 35 has completed a revolution a dog 41 thereon trips a latch 7 holding the lever 5 and allows a spring 8 to swing the lever and move the belt 6 on to the loose pulley 4. simultaneously applying a brake 9 to the pulley 3 to stop the machine. If a thread is to be completed with only a fraction of the steps on the cam 35, more than one dog 41 is provided thereon. The cam plate 18 may have its sides provided with different inclinations, as shown in Fig. 2 for producing threads of different pitch and is then indexed with the required side adjacent the roller 42 by means of cross grooves 18<SP>1</SP> thereon and a vertical key 14' on the slide 14, clamping being effected by a screw 16. The sides may each have straight portions of different inclination for producing adjacent threads on the work of different pitch or may be curved for producing threads of varying pitch. The pitch may also be altered by driving the cam 12 from the work spindle 2 at one of three speeds obtained through a change speed gear. For intermediate thread pitches, the plate 18 may be replaced by an arm whose inclination to the vertical may be adjusted by a sector scale-and-vernier and micrometer screws. The total depth of the thread may be varied by adjusting the roller 27 nearer or farther from the point of the lever 33 but the proportions of the cut taken at each traverse remain the same, due to the steps of the :cam 35. The axial position of the tool relatively to the work is determined by adjusting the roller 42 vertically, relatively to the cam plate 18, with the roller 13 on the highest point of the cam 12, while adjustment of the tool relatively to the saddle 23, effected by a screw 47, with the roller at the lowest point of the cam 12 determines the commencement of the thread on the work. The work may be mounted between head and tailstock centres or the spindle 2 may be hollow to receive the work. The screw-cutting mechanism may be an attachment to an existing lathe.